CN113281352A - Resonant microwave moisture detection device and method based on frequency sweep technology - Google Patents
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Abstract
The invention discloses a resonant microwave moisture detection device and method based on a frequency sweep technology, wherein the resonant microwave moisture detection device comprises a microwave processing board, a power supply board, a microwave excitation cavity and a microwave resonant cavity, wherein the power supply board is used for supplying power to the microwave processing board; the microwave excitation cavity and the microwave resonant cavity are oppositely arranged at intervals to form a medium area for the material to be detected to pass through; the microwave excitation cavity is provided with a 1G transmitting probe, a 3G transmitting probe and a receiving probe; the microwave processing board comprises an MCU, a base frequency generator, a frequency sweep, a power amplifier, a frequency synthesizer, a digital switch, a 1G filter, a 3G filter, a detector, a receiving amplifier, an AD conversion module and a DA conversion module. The invention adopts the measurement of the offset of the resonant frequency point of the microwave resonant cavity to indicate the water content of the object, and uses the sweep frequency technology to quickly find the resonant frequency point, thereby improving the detection precision and efficiency.
Description
Technical Field
The invention belongs to the technical field of microwave application, and particularly relates to a resonant microwave moisture detection device and method based on a frequency sweep technology.
Background
At present, there are many ways to measure the moisture on the surface of an object, such as measuring the moisture by an infrared reflection method or measuring the moisture by a microwave moisture meter.
The infrared reflection is used for measuring the moisture content, and the moisture content is reflected by the difference of the different moisture contents of the object to the infrared reflectivity with specific wavelength. For example, chinese patent publication No. CN2150555Y discloses an infrared reflection moisture meter for measuring moisture of solid materials, which includes a light source, a monochromator, a light path device, and a measuring device. But infrared reflection mainly occurs on the surface of an object, and only an object with a flat surface and small thickness can be measured.
At present, most microwave moisture meters calculate the signal attenuation and phase offset of microwaves to obtain the moisture content of a measured object, the measured object with a specific thickness is calibrated in the early stage to fit data, and the measured object is often inconsistent in thickness in the production process, so that the measurement result is inaccurate.
For example, chinese patent publication No. CN103399022A discloses an online microwave moisture detection method and system for cigarette packets, which includes: (1) acquiring the moisture in tobacco bale leaves; (2) obtaining attenuation A and phase difference P measurement components of the online microwave moisture measurement device; (3) and establishing a mathematical model of the measurement components of the internal moisture, the attenuation A and the phase difference P, and predicting the internal moisture of the cigarette packet by using the mathematical model. However, when an article having a large thickness is measured, the signal amplitude is severely attenuated, and the measured phase error becomes large.
Meanwhile, the distance from the object to be measured to the microwave source affects the signal amplitude, and a distance measuring sensor is added to improve the precision.
In addition, the temperature of the microwave cavity changes, which causes signal phase shift. The temperature sensor is used for measuring the temperature of the cavity and the temperature compensation value is obtained by utilizing a known heating experiment, so that the influence caused by the temperature can be eliminated, but the compensation value is inconsistent due to the difference of the characteristics of each cavity, and each cavity needs to be corrected by a re-heating test. In industrial application, the cavity may need to move, the temperature of the passing position is high, the temperature sensor does not react fast enough, the fluctuation is also high, and the deviation caused by the temperature cannot be eliminated correctly in high-speed movement.
Disclosure of Invention
The invention provides a resonant microwave moisture detection device and method based on a frequency sweep technology, which are used for indicating the moisture content of an object by measuring the resonance frequency point offset of a microwave resonant cavity, and can improve the detection precision and efficiency by quickly finding out the resonance frequency point by using the frequency sweep technology.
A resonant microwave moisture detection device based on sweep frequency technology comprises a microwave processing board, a power supply board, a microwave excitation cavity and a microwave resonant cavity, wherein the power supply board is used for supplying power to the microwave processing board; the microwave excitation cavity and the microwave resonant cavity are oppositely arranged at intervals to form a medium area for the material to be detected to pass through; the microwave excitation cavity is provided with a 1G transmitting probe, a 3G transmitting probe and a receiving probe;
the microwave processing board comprises an MCU, a base frequency generator, a frequency sweep, a power amplifier, a frequency synthesizer, a digital switch, a 1G filter, a 3G filter, a detector, a receiving amplifier, an AD conversion module and a DA conversion module;
the MCU is used for controlling the output of the frequency sweep device and the fundamental frequency generator, the channel selection of the digital switch, the output of the DA conversion module and storing and processing the digital signals sent by the AD conversion module;
the fundamental frequency generator is used for receiving a control signal of the MCU and outputting a 900Mhz or 2900Mhz signal;
the frequency sweep device is used for receiving a control signal of the MCU and outputting a microwave signal from frequency P to frequency Q within set time;
the power amplifier is used for amplifying the microwave signal output by the frequency scanner;
the frequency synthesizer is used for synthesizing the output signal of the fundamental frequency generator and the microwave signal amplified by the power amplifier into a signal with final frequency;
the digital switch receives a control signal of the MCU and connects the frequency synthesizer to the 1G filter or the 3G filter; the 1G filter is connected with the 1G emission probe, and the 3G filter is connected with the 3G emission probe;
the signal received by the receiving probe is converted into a digital signal and stored in the MCU memory after passing through the wave detector, the receiving amplifier and the AD conversion module in sequence; and the DA conversion module is connected with the output end of the MCU. The DA conversion module is controlled by the MCU and outputs 0-20mA current to the outside.
The invention also provides a microwave moisture detection method, which uses the resonance type microwave moisture detection device and comprises the following steps:
(1) under the no-load state of the medium area, the MCU controls the fundamental frequency generator to generate a 900Mhz signal; then the MCU controls the frequency sweep device to sweep frequency from a frequency a1 to a frequency a2, and simultaneously, the AD conversion module is started;
the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 900Mhz signal to the frequency mixer to generate a frequency signal near 1Ghz, and the signal enters a 1G transmitting channel through the digital switch; after passing through a 1G channel filter and being amplified, the 1G emission probe radiates to the resonant cavity;
the signal is received by the receiving probe through the resonant cavity, is input into the receiving amplifier after passing through the detector, and is converted into a digital signal to be stored in the MCU memory through the AD conversion module; calculating a resonance frequency A corresponding to the maximum signal amplitude point by processing the stored data;
(2) the MCU controls the fundamental frequency generator to generate 2900Mhz signals, then the MCU controls the frequency sweep device to sweep frequency from b1 to b2, and simultaneously the AD conversion module is started;
the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 2900Mhz signal to the frequency mixer to generate a frequency signal near 3Ghz, and the signal enters a 3G transmitting channel through the digital switch; after passing through a 3G channel filter and being amplified, the signal is radiated to a resonant cavity by a 3G transmitting probe;
the signal is received by the receiving probe through the resonant cavity, is input into the receiving amplifier after passing through the detector, and is converted into a digital signal to be stored in the MCU memory through the AD conversion module; calculating a resonance frequency B corresponding to the maximum signal amplitude point by processing the stored data;
(3) putting a material to be detected into a medium area, and repeating the processes of the step (1) and the step (2) to obtain the resonant frequency Ax of the 1G channel and the resonant frequency Bx of the 3G channel in a detection state;
(4) and calculating the resonance deviation value under the detection state as relative water content, converting the resonance deviation value into a coding value of current, outputting the coding value to an external PC (personal computer) end through a DA (digital-to-analog) conversion module, converting a current signal into a digital coding value by the PC end, and calculating the water content of the material to be detected by using an externally-matched quantitative meter.
The method can accurately measure the water content of the material to be measured, and the gram weight of the object to be measured is measured by using a high-precision thickness gauge matched with the periphery of the material to be measured, and then the measured water content gram weight is reduced, so that the gram weight and the water content of the object can be obtained.
In order to accurately measure the water content, the invention adopts the measurement of the offset of the resonant frequency point of the microwave resonant cavity to indicate the water content of the object. Two frequency points of the resonant cavity are used, the 1G offset of the resonant frequency point indicates the moisture content of the measured object, and the 3G offset of the resonant frequency point is used for eliminating the physical characteristic change of the cavity. And rapidly finding the resonant frequency point by using a frequency sweeping technology.
In the step (1), the MCU controls the frequency sweep device to sweep frequency from 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; signals sent by the frequency scanner pass through the amplifier and then are mixed with 900Mhz signals to the frequency mixer to generate frequency signals from 1G to 1.03G; at this time, the measured resonant frequency a of the no-load 1G channel is:
A＝[(a2-a1)/1000]*Ta+a1
a1 and a2 are respectively 100Mhz and 130Mhz, which represent the lower limit and the upper limit of the scanning frequency, a1 to a2 are divided into 1000 steps, Ta is the point corresponding to the highest point of the voltage value of the waveform in the 1000 steps, and the corresponding frequency is the resonant frequency of the 1G channel.
Preferably, in step (1), after obtaining the resonant frequency a of the no-load 1G channel, the method further includes:
the frequency sweep device is changed to start from the frequency (A-3) Mhz to the frequency (A +3) Mhz, the scanning step is 6Khz, the scanning time is 2ms, the resonant frequency A2 is finally obtained, and the value of the resonant frequency A of the 1G channel in idle load is updated to be A2. By this preferred procedure, the accuracy of the resonant frequency of the 1G channel at idle can be improved.
The MCU controls the frequency scanner to sweep frequency from 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 2900Mhz signal to the frequency mixer to generate a frequency signal from 3G to 3.03G; at this time, the measured resonant frequency of the 3G channel at no load is represented by the following formula:
B＝[(b2-b1)/1000]*Tb+b1
b1 and b2 are respectively 100Mhz and 130Mhz and represent the lower limit and the upper limit of the scanning frequency, b1 to b2 are divided into 1000 steps, Tb is the point corresponding to the highest point of the voltage value of the waveform in the 1000 steps, and the corresponding frequency is the resonant frequency of the 3G channel.
Preferably, in the step (2), after obtaining the resonant frequency B of the 3G channel during idle time, the method further includes:
and changing the frequency sweep of the frequency sweep device from the frequency (B-3) Mhz to the frequency (B +3) Mhz, scanning the frequency step by 6Khz, scanning the frequency step by 2ms, finally obtaining the resonant frequency B2, and updating the value of the resonant frequency B of the 3G channel in idle load to be B2. By this preferred procedure, the resonant frequency accuracy of the 3G channel at idle can be improved.
In the step (4), the calculation formula of the resonance deviation value is as follows:
Y＝Ax–A–N*(Bx–B)
in the formula, Y represents a resonance offset value, and N represents a compensation coefficient.
The encoded value formula for converting the resonance offset value to a current is:
I＝Y*M
wherein Y is a resonance deviation value, which is equal to the relative water content of the object; m is a sensitivity value which is less than or equal to 1 and is used for adjusting the current output and avoiding saturation when measuring large moisture, and the parameter is set to be 0.7 by a PC in a default mode; the DA conversion module outputs a 0-20mA current signal according to the coded value I of the current. The coding value of the current is 0-4095, corresponding to the current signal of 0-20mA outputted by the DA conversion module.
The formula for calculating the water content of the material to be measured is as follows:
V＝100*K*i/D+b
in the formula, V represents the water content; k and b are both correction coefficients and are obtained through actual calibration; i is a digital coding value converted from a current signal transmitted by the instrument by the PC end; d represents the mass of the measured material and is provided by an external dosing scale.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention uses the frequency sweep function, sends out the excitation microwave signal of specific frequency P to specific frequency Q to the cavity within certain time, form a continuously variable voltage signal waveform after reclaiming the signal on the excitation cavity, the time axis that the voltage value peak of the waveform corresponds to is the resonance frequency point this time, because the excitation microwave frequency and cavity resonant frequency will be resonated, relative to other frequency, the signal amplitude attenuation of the resonant frequency is very small.
2. The invention adopts the measurement of the offset of the resonance frequency point of the microwave resonant cavity to indicate the water content of the object. Two frequency points of the resonant cavity are used, the 1G offset of the resonant frequency point indicates the moisture content of the measured object, and the 3G offset of the resonant frequency point is used for eliminating the physical characteristic change of the cavity. The frequency sweeping technology is used for rapidly finding out the resonant frequency point, so that the detection efficiency and the detection precision are improved.
3. The invention uses the self-adaptive microwave transmitting power, when measuring articles with large thickness, the signal amplitude is seriously attenuated, the transmitting power can be improved, and the signal amplitude can be properly increased, thereby improving the accuracy when positioning the resonance frequency point.
Drawings
Fig. 1 is a schematic structural diagram of a resonant microwave moisture detection device based on a frequency sweep technique.
FIG. 2 is a schematic view of the structure of the microwave processing plate according to the present invention.
Fig. 3 is a 1G channel 30M bandwidth sweep waveform diagram.
Fig. 4 is a 1G channel 6M bandwidth sweep waveform diagram.
Fig. 5 is a diagram of a 3G channel 30M bandwidth sweep waveform.
Fig. 6 is a 3G channel 6M bandwidth sweep waveform diagram.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.
The invention is mainly based on the microwave resonance principle, as shown in figure 1, a resonance type microwave moisture detection device based on the sweep frequency technology comprises a microwave processor 3, a power panel, a microwave excitation cavity 1 and a microwave resonant cavity 2. Wherein, the microwave processor 3 is arranged on the outer wall of the microwave excitation cavity 1, and the power panel (not shown in the figure) is used for supplying power to the microwave processing panel 1. The microwave excitation cavity 1 and the microwave resonant cavity 2 are oppositely and separately arranged to form a medium area for the material to be detected to pass through. The microwave excitation cavity 1 is provided with a 1G transmitting probe 4, a 3G transmitting probe 5 and a receiving probe 6. The microwave processor 3 is provided with three SM3.5 coaxial seats which are connected with a 1G transmitting probe 4, a 3G transmitting probe 5 and a receiving probe 6 of the microwave excitation cavity 1 through coaxial lines.
The microwave resonant cavity 2 is a resonant element working at microwave frequency, and forms an electromagnetic oscillation medium area in and between the two cavity bodies, and when the medium is fixed, the specific oscillation frequency is unchanged. When the medium (such as the object to be measured) between the two cavities is changed, the specific oscillation frequency of the medium is changed.
As shown in fig. 2, the microwave processing board 3 includes an MCU chip 31, a fundamental frequency generator 32, a frequency scanner 33, a power amplifier 34, a frequency synthesizer 35, a digital switch 36, a 1G filter 37, a 3G filter 38, a detector 39, a receiving amplifier 40, an AD conversion module 41, and a DA conversion module 42.
Specifically, the MCU chip 31 employs a 32-bit ARM single chip with a main frequency of 100M.
The fundamental frequency generator 32 is used to provide a 900M signal and a 2900M signal.
The frequency sweep device 33: microwave signals from a set frequency P to a set frequency Q can be generated within a specified time, the set frequency P and the set frequency Q are adjustable, and the signal power is adjustable. The set frequency P and the set frequency Q are maintained in 1000 steps.
The power amplifier 34 is used for amplifying the microwave signal from the frequency scanner 33.
The frequency synthesizer 35 is used to synthesize the output signal of the fundamental frequency generator 32 and the output signal of the frequency scanner 33 into a signal of the final frequency.
The digital switch 36 is controlled by the MCU chip 31 to selectively connect the frequency synthesizer 35 to the 1G channel or the 3G channel.
The 1G filter 37 is used to filter out frequency signals other than 970M to 1030M.
The 1G transmission probe 4 is used to radiate a 1G channel microwave signal to the cavity and the medium.
The 3G filter 38 is used to filter out frequency signals other than 2800M to 3400M.
The 3G transmission probe 5 is used to radiate a microwave signal of the 3G channel to the cavity and the medium.
The receiving probe 6 is used for receiving the microwave signal in the cavity.
The detector 39 is used to hold the dc part signal using a detector diode.
The receive amplifier 40 is used to amplify the detected signal.
The AD conversion module 41 is configured to convert the voltage signal output by the detector 39 into a digital signal.
The DA conversion module 42 is used for converting the measured relative water content into a corresponding current value and outputting the current value to an external device.
In operation, the microwave processor 3 sends out a specific frequency excitation microwave signal to the cavity through the sending probe arranged on the microwave excitation cavity 1, the signal passes through the intermediate medium and the microwave resonant cavity 2, the signal is recovered by the receiving probe 6 on the microwave excitation cavity 1 and passes through the wave detector 39 to form a voltage signal which is input into the microwave processor, and the voltage signal is converted into a digital value in the processor through the AD module. And similarly, a scanning function is used, an excitation microwave signal with specific frequency P to specific frequency Q is sent out to the cavity within a certain time, a continuously-changed voltage signal waveform is formed after the signal is recovered on the excitation cavity, the time axis corresponding to the highest point of the voltage value of the waveform is the resonant frequency point, the excitation microwave frequency and the cavity resonant frequency are the same and the signal amplitude of the resonant frequency is greatly attenuated compared with other frequencies.
The following describes the use process of the resonant microwave moisture detection device according to the actual use scenario. The invention carries out mode control through the instrument, and the instrument has a debugging mode, a correcting mode and a working mode.
Debugging mode: the setting instrument 1G channel transmits minimum and maximum power, and the 3G channel transmits minimum and maximum power is provided. Provides 1G and 3G broadband frequency sweeping functions, and sends the signals to a PC through a communication line and displays a waveform diagram.
And (3) correction mode: the resonance frequency a around 1G and the resonance frequency B around 3G at no load were measured.
The working mode is as follows: a moisture measuring step and an external influence value measuring step are provided.
The method comprises the following specific steps: before first power-on, the communication line of the moisture meter is connected to the PC, debugging software is started, then the power-on is carried out, the moisture meter sends debugging information to the PC, the PC sends back response information, and the moisture meter enters a debugging mode. In the commissioning mode, the maximum and minimum transmit power of the 1G channel may be limited by the 1G high range output and the 1G low range output. The maximum and minimum transmit power of the 3G channel is limited by the 3G high range output and the 3G low range output. After clicking the No. 1 scanning key, the MCU controls the fundamental frequency generator to generate a 900Mhz signal, then the MCU controls the frequency scanner to start frequency scanning from the frequency of 100Mhz to 130Mhz, the scanning step is 30Khz, the scanning time is 2ms, and simultaneously the AD conversion is started. Signals sent by the frequency scanner pass through the amplifier and then are mixed with 900Mhz signals to the mixer, 1G to 1.03G frequency signals can be generated, and the signals enter a 1G transmitting channel through the digital switch. After passing through the 1G channel filter and being amplified, the 1G probe radiates to the cavity. The signal is detected by the receiving probe through the resonant cavity, then input to the receiving amplifier, and finally converted into a digital signal by the AD module and stored in the MCU memory. And finally, transmitting the stored digital signals to a PC (personal computer) through a communication line, and displaying the sweep frequency oscillogram on debugging software.
After clicking the No. 2 scanning key, the MCU controls the fundamental frequency generator to generate 2900Mhz signals, then the MCU controls the frequency scanner to start frequency scanning from the frequency of 100Mhz to 130Mhz, the scanning step is 30Khz, the scanning time is 2ms, and meanwhile AD conversion is started. The signal sent by the frequency scanner passes through the amplifier and then is mixed with 2900Mhz signal to the mixer, so that 3G to 3.03G frequency signal can be generated, and the signal enters a 3G transmitting channel through the digital switch. After passing through a 3G channel filter and being amplified, the 3G probe radiates to the cavity. The signal is detected by the receiving probe through the resonant cavity, then input to the receiving amplifier, and finally converted into a digital signal by the AD module and stored in the MCU memory. And finally, transmitting the stored digital signals to a PC (personal computer) through a communication line, and displaying the sweep frequency oscillogram on debugging software.
And clicking the working key to enable the moisture meter to enter a correction mode. Firstly, measuring moisture, wherein the MCU controls the frequency sweep device to sweep frequency from 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; signals sent by the frequency scanner pass through the amplifier and then are mixed with 900Mhz signals to the mixer to generate frequency signals from 1G to 1.03G, a waveform diagram obtained after processing is shown in figure 3, and a primary resonant frequency A1 is obtained. And (3) executing the step of measuring moisture again, changing the frequency sweep of the frequency sweep device from the frequency (A1-3) Mhz to the frequency (A1+3) Mhz, scanning the frequency sweep device with the scanning step of 6Khz and the scanning time of 2ms to obtain a waveform diagram as shown in the figure 4, and finally obtaining that the precision of the resonant frequency A2 is improved by 5 times compared with the precision of A1.
Then, measuring an external influence value, wherein the MCU controls the frequency scanner to sweep frequency from 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; signals sent by the frequency scanner pass through the amplifier and then are mixed with 2900Mhz signals to the mixer, so that frequency signals from 3G to 3.03G are generated, a waveform diagram is obtained after processing, and a primary resonant frequency B1 is obtained first, as shown in FIG. 5. And the step of measuring the external influence value is executed again, the frequency sweep of the frequency sweep device is changed from the frequency (B1-3) Mhz to the frequency (B1+3) Mhz, the scanning step is 6Khz, the scanning time is 2ms, a waveform diagram obtained after processing is shown in fig. 6, and finally the precision of the obtained resonant frequency B2 is improved by 5 times compared with that of B1. A2 and B2 are respectively used as resonance frequency points of the 1G channel and the 3G channel in no-load.
In FIGS. 3-6, the Y-axis is the voltage value of the waveform (0-65535), corresponding to 0-5V; the X-axis is the time axis 1-1000. It can be seen that the accuracy of the resonant frequency can be greatly improved by further scanning with a 6M bandwidth after scanning with a 30M bandwidth.
And then the moisture meter automatically enters a working mode, in the working mode, the steps of measuring moisture and measuring external influence values are sequentially executed, and the resonance deviant is obtained and then converted into current to be output to the periphery. In the process, the center frequency and the bandwidth of the frequency scanner are automatically changed, the resonance point of the frequency sweep is kept to be positioned near the center frequency of the frequency sweep, when the moisture suddenly changes and the current 6M frequency sweep bandwidth does not measure the resonance point, the 30M frequency sweep bandwidth is used for measuring the resonance point immediately, then the center frequency point is adjusted, and the 6M frequency sweep bandwidth is reused for detecting the resonance frequency point. When the moisture content is low, and the amplitude of the waveform detected by the sweep frequency exceeds a preset value, the transmitting power is reduced. When the moisture content is large, and the amplitude of the waveform detected by the sweep frequency is lower than a preset value, the transmitting power is increased.
In the actual detection process, after the debugging is finished, the conventional steps are as follows: after being electrified, the power supply directly enters a correction mode, and after correction, the power supply enters a working mode.
Finally, the DA conversion module converts the measured relative water content into corresponding current and outputs the current to external equipment. Calculating the water content formula of the material to be measured according to the current as follows:
V＝100*K*i/D+b
in the formula, V represents the water content; k and b are both correction coefficients and are obtained through actual calibration; i is a digital coding value converted from a current signal transmitted by the instrument by the PC end; d represents the mass of the material being measured and is typically recorded in an external scale after measurement in advance.
The effects of the present invention are verified by specific experimental data below.
Table 1 below is a moisture table of a4 paper after testing, and the relative moisture content of the paper is indirectly represented by the current output recorded at 23 degrees celsius with a sensitivity M of 0.7. The correlation of the output of the moisture meter with the relative moisture content for different amounts of A4 paper is 0.99735195, which shows that the measurement accuracy is kept higher and the measurement effect is better as the thickness of the A4 paper is increased.
TABLE 1
The following table 2 is a moisture table of the special paper after testing, and the relative water content of the paper is indirectly reflected by the current output value recorded at the temperature of 23 ℃ and the sensitivity M of 0.7. For different amounts of specialty paper, the correlation of the output relative water content of the water meter is 0.998679122, which shows that as the thickness of the specialty paper increases, higher measurement accuracy is maintained and better measurement effect is achieved.
TABLE 2
Table 3 below shows the current output value with the sensitivity M being 0.7 in the idle state at different temperatures, and it can be seen that the current output value has a small change at different temperatures. By the method of the invention, the influence of temperature is compensated, thereby eliminating the influence caused by temperature change.
TABLE 3
| No-load state of moisture meter | PC terminal measuring current coding value |
| 23℃ | 4 |
| 28℃ | 7 |
| 32 |
6 |
| 37 |
5 |
| 42 |
5 |
| 47 |
5 |
| 52℃ | 4 |
| 57℃ | 4 |
| 62 |
5 |
| 67 |
3 |
The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.
Claims (8)
1. A resonant microwave moisture detection device based on sweep frequency technology is characterized by comprising a microwave processing board, a power supply board, a microwave excitation cavity and a microwave resonant cavity, wherein the power supply board is used for supplying power to the microwave processing board; the microwave excitation cavity and the microwave resonant cavity are oppositely arranged at intervals to form a medium area for the material to be detected to pass through; the microwave excitation cavity is provided with a 1G transmitting probe, a 3G transmitting probe and a receiving probe;
the microwave processing board comprises an MCU, a base frequency generator, a frequency sweep, a power amplifier, a frequency synthesizer, a digital switch, a 1G filter, a 3G filter, a detector, a receiving amplifier, an AD conversion module and a DA conversion module;
the MCU is used for controlling the output of the frequency sweep device and the fundamental frequency generator, the channel selection of the digital switch, the output of the DA conversion module and storing and processing the digital signals sent by the AD conversion module;
the fundamental frequency generator is used for receiving a control signal of the MCU and outputting a 900Mhz or 2900Mhz signal;
the frequency sweep device is used for receiving a control signal of the MCU and outputting a microwave signal from frequency P to frequency Q within set time;
the power amplifier is used for amplifying the microwave signal output by the frequency scanner;
the frequency synthesizer is used for synthesizing the output signal of the fundamental frequency generator and the microwave signal amplified by the power amplifier into a signal with final frequency;
the digital switch receives a control signal of the MCU and connects the frequency synthesizer to the 1G filter or the 3G filter; the 1G filter is connected with the 1G emission probe, and the 3G filter is connected with the 3G emission probe;
the signal received by the receiving probe is converted into a digital signal and stored in the MCU memory after passing through the wave detector, the receiving amplifier and the AD conversion module in sequence; the DA conversion module is controlled by the MCU and outputs 0-20mA current to external equipment.
2. A microwave moisture detection method using the resonance type microwave moisture detection device according to claim 1, comprising the steps of:
(1) under the no-load state of the medium area, the MCU controls the fundamental frequency generator to generate a 900Mhz signal; then the MCU controls the frequency sweep device to sweep frequency from a frequency a1 to a frequency a2, and simultaneously, the AD conversion module is started;
the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 900Mhz signal to the frequency mixer to generate a frequency signal near 1Ghz, and the signal enters a 1G transmitting channel through the digital switch; after passing through a 1G channel filter and being amplified, the 1G emission probe radiates to the resonant cavity;
the signal is received by the receiving probe through the resonant cavity, is input into the receiving amplifier after passing through the detector, and is converted into a digital signal to be stored in the MCU memory through the AD conversion module; calculating a resonance frequency A corresponding to the maximum signal amplitude point by processing the stored data;
(2) the MCU controls the fundamental frequency generator to generate 2900Mhz signals, then the MCU controls the frequency sweep device to sweep frequency from b1 to b2, and simultaneously the AD conversion module is started;
the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 2900Mhz signal to the frequency mixer to generate a frequency signal near 3Ghz, and the signal enters a 3G transmitting channel through the digital switch; after passing through a 3G channel filter and being amplified, the signal is radiated to a resonant cavity by a 3G transmitting probe;
the signal is received by the receiving probe through the resonant cavity, is input into the receiving amplifier after passing through the detector, and is converted into a digital signal to be stored in the MCU memory through the AD conversion module; calculating a resonance frequency B corresponding to the maximum signal amplitude point by processing the stored data;
(3) putting a material to be detected into a medium area, and repeating the processes of the step (1) and the step (2) to obtain the resonant frequency Ax of the 1G channel and the resonant frequency Bx of the 3G channel in a detection state;
(4) and calculating the resonance deviation value under the detection state as relative water content, converting the resonance deviation value into a coding value of current, outputting the coding value to an external PC (personal computer) end through a DA (digital-to-analog) conversion module, converting a current signal into a digital coding value by the PC end, and calculating the water content of the material to be detected by using an externally-matched quantitative meter.
3. The microwave moisture detection method according to claim 2, wherein in the step (1), the MCU controls the frequency sweep device to sweep from frequency 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; signals sent by the frequency scanner pass through the amplifier and then are mixed with 900Mhz signals to the frequency mixer to generate frequency signals from 1G to 1.03G; at this time, the measured resonant frequency a of the no-load 1G channel is:
A＝[(a2-a1)/1000]*Ta+a1
a1 and a2 are respectively 100Mhz and 130Mhz, which represent the lower limit and the upper limit of the scanning frequency, a1 to a2 are divided into 1000 steps, Ta is the point corresponding to the highest point of the voltage value of the waveform in the 1000 steps, and the corresponding frequency is the resonant frequency of the 1G channel.
4. A microwave moisture detecting method according to claim 3, wherein in the step (1), after obtaining the resonant frequency a of the 1G channel during idle time, the method further comprises:
the frequency sweep device is changed to start from the frequency (A-3) Mhz to the frequency (A +3) Mhz, the scanning step is 6Khz, the scanning time is 2ms, the resonant frequency A2 is finally obtained, and the value of the resonant frequency A of the 1G channel in idle load is updated to be A2.
5. The microwave moisture detection method according to claim 2, wherein in the step (2), the MCU controls the frequency sweep device to sweep from a frequency of 100Mhz to 130Mhz, the scanning step is 30Khz, and the scanning time is 2 ms; the signal sent by the frequency sweep device passes through the amplifier and then is mixed with a 2900Mhz signal to the frequency mixer to generate a frequency signal from 3G to 3.03G; at this time, the measured resonant frequency of the 3G channel at no load is represented by the following formula:
B＝[(b2-b1)/1000]*Tb+b1
b1 and b2 are respectively 100Mhz and 130Mhz and represent the lower limit and the upper limit of the scanning frequency, b1 to b2 are divided into 1000 steps, Tb is the point corresponding to the highest point of the voltage value of the waveform in the 1000 steps, and the corresponding frequency is the resonant frequency of the 3G channel.
6. The microwave moisture detecting method according to claim 5, wherein the step (2), after obtaining the resonant frequency B of the 3G channel during idle time, further comprises:
and changing the frequency sweep of the frequency sweep device from the frequency (B-3) Mhz to the frequency (B +3) Mhz, scanning the frequency step by 6Khz, scanning the frequency step by 2ms, finally obtaining the resonant frequency B2, and updating the value of the resonant frequency B of the 3G channel in idle load to be B2.
7. A microwave moisture detecting method according to claim 2, wherein in the step (4), the resonance shift value is calculated by the formula:
Y＝Ax–A–N*(Bx–B)
in the formula, Y represents a resonance offset value, and N represents a compensation coefficient.
8. A microwave moisture detection method according to claim 7 wherein in step (4) the resonant offset value is converted to a coded value of current by the formula:
I＝Y*M
wherein Y is a resonance deviation value, which is equal to the relative water content of the object; m is a sensitivity value which is less than or equal to 1 and is used for adjusting the current output and avoiding saturation when measuring large moisture; the DA conversion module outputs a 0-20mA current signal according to the coded value I of the current;
the formula for calculating the water content of the material to be measured is as follows:
V＝100*K*i/D+b
in the formula, V represents the water content; k and b are both correction coefficients and are obtained through actual calibration; i is a digital coding value converted from a current signal transmitted by the instrument by the PC end; d represents the mass of the measured material and is provided by an external dosing scale.
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